Overcharged and no one cares

I was charged different prices at the checkout than the price on the shelf in 2 different stores on two different days with different products. I logged a complaint under my online profile on their website a week ago, but no one has responded. Being overcharged by almost 50% for an item that a large consumer base buys (like Weet-Bix) and no-one lifting a finger about it is gravely concerning.